| 摘要 |
An apparatus for testing the insulation of an insulated electrical conductor has an alternating current high voltage power source which provides a high test voltage between the electrical conductor and an electrode to reveal defects in the insulation. A high Q antiresonant circuit, tuned to a predetermined frequency, is connected in series with the electrode and power source for shunting most frequency components of the corona and noise currents to ground and for non-shunting an insulation fault voltage of the predetermined frequency resulting from an arc current due to a defect in the insulation. The fault voltage signal non-shunted by the antiresonant circuit is provided through a coupling impedance to a transmission cable having a pair of twisted wires for transmission to a remote location. Impedance matching transformers, coupled to both pairs of ends of the twisted wires, are tuned to the same frequency as the antiresonant circuit to minimize attenuation of the signal. The control portion includes a detecting circuit for generating a fault indication signal in response to the voltage signal transmitted to the control portion exceeding a variable threshold value. A negative bias circuit provides a negative DC voltage dependent upon the voltage of the high test voltage to the control portion for defining the threshold voltage value.
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